1. Field of the Invention
The present invention relates to a fuel cell apparatus for generating electric power through a reaction between a fuel and an oxidizer, and more specifically to a fuel cell apparatus having a fuel storage unit and fuel flow path.
2. Related Background Art
A fuel cell includes, as an electric power generation unit, a membrane electrode assembly in which an electrolyte membrane is interposed between a fuel electrode containing a catalyst and an oxidizer electrode containing a catalyst. In the membrane electrode assembly, a fuel such as a hydrogen gas is fed to the fuel electrode side, and an oxidizer such as an oxygen gas is fed to the oxidizer electrode side to perform an electrochemical reaction of the fuel and the oxidizer through the electrolyte membrane.
Recently, fuel cells are expected to be used for small electrical instruments such as digital cameras and laptop computers. This is because a fuel cell may feed an amount of energy per volume of several to about ten times that of a conventional battery, and thus may allow continuous use of the small electrical instruments for a long time by supplying a fuel.
In such portable fuel cells, a fuel required for electric power generation such as hydrogen is held in a fuel tank or the like, which is separate from the electric power generation unit. The fuel in the fuel tank is fed to the electric power generation unit through a fuel flow path. In a case where a fuel is consumed in electric power generation, the fuel is filled or the fuel tank is exchanged. For exchange of the fuel tank, the fuel tank must be removed from a fuel cell body once.
For example, in a fuel cell apparatus using a gas as a fuel, atmospheric air may mix into the fuel flow path during exchange of the fuel tank. Mixing of the atmospheric air into the fuel flow path causes significant reduction in power output of the fuel cell, and thus the gas in the fuel flow path must be replaced with a fuel gas after the exchange of the fuel tank.
Further, in a fuel cell using an aqueous solution of methanol or the like as a fuel, a methanol concentration in a vicinity of the fuel electrode may decrease due to electric power generation. In this case, the methanol solution in the flow path must be replaced with a fresh methanol solution.
For example, Japanese Patent Application Laid-Open No. 2003-331888 discloses a method of replacing a gas in a fuel flow path, including: feeding a fuel gas; and discharging the fuel gas from a hydrogen replacement valve.
However, in the above-described method, a volume of fuel consumed in gas replacement may reach several times the volume of the fuel flow path. Such fuel consumption due to gas replacement causes reduction in amount of energy obtained through power generation in a fuel cell.